I got my rebuilt 455 running,,,I changed over to a HEI system..What plug gap should I run ...And the timing I beleive is set at 10 per manual,,would this change going to a HEI system..

 

I am not an expert but I am running .044 gap on the plugs, and 38 degrees total timing all in by 3 grand. 18 degrees initial timing. If you have an above stock cam, the timing in the manual will not be the same.
I use a dial back timing light to set mine also.

 

I am using a stock cam

 

I am running a .045 gap on my plugs with 14 degrees initial timing and a total of 36 all in by 3000 in my 442. I have a 10 degree advance can on the HEI. I set it up for the best performance. A little trial and error can make a big performance difference.